Scoring concept terms using a deep network

ABSTRACT

Methods, systems, and apparatus, including computer programs encoded on computer storage media, for scoring concept terms using a deep network. One of the methods includes receiving an input comprising a plurality of features of a resource, wherein each feature is a value of a respective attribute of the resource; processing each of the features using a respective embedding function to generate one or more numeric values; processing the numeric values to generate an alternative representation of the features of the resource, wherein processing the floating point values comprises applying one or more non-linear transformations to the floating point values; and processing the alternative representation of the input to generate a respective relevance score for each concept term in a pre-determined set of concept terms, wherein each of the respective relevance scores measures a predicted relevance of the corresponding concept term to the resource.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/802,184, filed on Mar. 13, 2013, the disclosure of which is herebyincorporated by reference in its entirety.

BACKGROUND

This specification relates to identifying concept terms that arerelevant to resources.

Internet resources (e.g., web pages, images, text documents, multimediacontent) may include content that describes any of a wide variety ofconcepts.

SUMMARY

In general, one innovative aspect of the subject matter described inthis specification can be embodied in methods that include the actionsof receiving an input comprising a plurality of features of a resource,wherein each feature is a value of a respective attribute of theresource; processing each of the features using a respective embeddingfunction to generate one or more numeric values; processing the numericvalues to generate an alternative representation of the features of theresource, wherein processing the floating point values comprisesapplying one or more non-linear transformations to the floating pointvalues; and processing the alternative representation of the input togenerate a respective relevance score for each concept term in apre-determined set of concept terms, wherein each of the respectiverelevance scores measures a predicted relevance of the correspondingconcept term to the resource.

Other embodiments of this aspect include corresponding computer systems,apparatus, and computer programs recorded on one or more computerstorage devices, each configured to perform the actions of the methods.

A system of one or more computers can be configured to performparticular operations or actions by virtue of having software, firmware,hardware, or a combination of them installed on the system that inoperation causes or cause the system to perform the actions. One or morecomputer programs can be configured to perform particular operations oractions by virtue of including instructions that, when executed by dataprocessing apparatus, cause the apparatus to perform the actions.

These and other embodiments can each optionally include one or more ofthe following features. Each of the embedding functions can be specificto features of a respective feature type. The method can further includeobtaining the plurality of features of the resource in response toreceiving an indication that an online advertisement auction is to beconducted to select one or more advertisements for inclusion in aparticular presentation of the resource. The method can further include:selecting one or more of the concept terms as advertising keywords to beused in selecting candidate advertisements for participation in theonline advertisement auction based on the relevance scores. The methodcan further include: filtering out concept terms that are not in thesame language as the resource. The method can further include: filteringout concept terms that have a Term Frequency Inverse Document Frequency(TF-IDF) score that exceeds a threshold value. The numeric values can befloating point values. The numeric values can be quantized integervalues, and wherein an encoding of the quantized integer valuesrepresents floating point values.

In general, another innovative aspect of the subject matter described inthis specification can be embodied in methods that include the actionsof obtaining data identifying training resources and one or morerespective associated concept terms for each of the training resources;specifying output criteria for a respective predicted output generatedby the classifier for each of the training resources; and training theembedding function layer, the neural network layers, and the classifierbased on respective features of each the training resources and on thespecified output criteria, wherein each feature is a value of arespective attribute of the resource.

Other embodiments of this aspect include corresponding computer systems,apparatus, and computer programs recorded on one or more computerstorage devices, each configured to perform the actions of the methods.

A system of one or more computers can be configured to performparticular operations or actions by virtue of having software, firmware,hardware, or a combination of them installed on the system that inoperation causes or cause the system to perform the actions. One or morecomputer programs can be configured to perform particular operations oractions by virtue of including instructions that, when executed by dataprocessing apparatus, cause the apparatus to perform the actions.

These and other embodiments can each optionally include one or more ofthe following features. The method can further include specifying that,for each training resource, relevance scores generated for concept termsassociated with the training resource should exceed relevance scoresgenerated for a random sample of other concept terms in the plurality ofconcept terms that are not associated with the training resource. Themethod can further include obtaining data identifying a trainingresource viewed by a user; obtaining data identifying an advertisementin a first resource selected by the user within a threshold time windowof viewing the training resource; and associating a keyword used inplacing the advertisement in the first resource with the trainingresource viewed by the user as a concept term.

Particular embodiments of the subject matter described in thisspecification can be implemented so as to realize one or more of thefollowing advantages. A deep network can be effectively used to predictconcept terms that are relevant to a resource. Once trained, the deepnetwork can be used to predict relevant concept terms for novelresources, i.e., resources that were not previously known to the deepnetwork. For example, the deep network can be used to select advertisingkeywords that are relevant to a resource. Using the deep network toselect advertising keywords may result in more relevant advertisementsbeing included in the resource, e.g., by increasing the relevance to theresource of the advertisements selected for participation in an onlineadvertising auction conducted to place one or more advertisements in theresource.

The details of one or more embodiments of the subject matter of thisspecification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages of thesubject matter will become apparent from the description, the drawings,and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example concept term scoring system.

FIG. 2 is a flow diagram of an example process for scoring conceptterms.

FIG. 3 is a flow diagram of an example process for training a conceptterm scoring system.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of an example concept term scoring system 100.The concept term scoring system 100 is an example of a systemimplemented as computer programs on one or more computers in one or morelocations, in which the systems, components, and techniques describedbelow can be implemented.

The concept term scoring system 100 receives an input and generates apredicted output based on the received input. In particular, the inputis a set of features of a resource and the output generated by theconcept term scoring system 100 based on the input is a respective scorefor each of a set of concept terms. The set of concept terms ispredetermined and represents concepts that have been determined to berelevant to the system or to a collection of resources. The scoresgenerated for the concept terms are predictions of how relevant each ofthe concept terms is to the resource. For example, the concept terms maybe keywords that are used to select advertisements for participation inonline advertisement auctions.

The features of the resource are values of respective attributes of theresource that characterize the resource in some way and can includefeatures of multiple respective categorically distinct feature types. Afeature of a particular type is a list of one or more active featureelements, i.e., a list of tokens or of token-value pairs, selected froma vocabulary of possible active feature elements of the feature type.For example, the tokens may be words in a natural language, e.g.,English, and the vocabulary for the feature type may be the known wordsin the natural language. The vocabularies for the feature types may beoverlapping or non-overlapping and the list for a given feature type maybe ordered or unordered.

For example, the concept term scoring system 100 can receive features120 from a feature data store 102. For example, the features 120 can befeatures of various feature types that have been extracted from aparticular resource in response to receiving an indication that anonline advertisement auction is to be conducted to select one or moreadvertisements to be included in a particular presentation of theresource. The features of the resource can include, e.g., any of: theuniform resource locator (URL) of the resource, the domain name of theresource, an identifier of the publisher of the resource, data obtainedby the concept scoring system 100 that identifies the categories orentity types that are relevant to the resource, terms that appear mostfrequently in the resource, and so on. The features of the resource canalso include features obtained from other systems or services thatsummarize the content or the utility of the resource, e.g., systems thatattempt to identify the most important terms in the resource, systemsthat identify entities that are relevant to the resource, and so on.

The concept term scoring system 100 uses the received input features topredict an output. The output can be stored in a scored concept termdata store 114 or used for some immediate purpose. In particular, theoutput is a vector of scores that includes a respective score for eachof the set of concept terms. In the online advertising context, forexample, where the input features are features of resource for which anonline advertisement auction is to be conducted, the concept termscoring system 100 can generate a score for each of a set of conceptterms that may be used as advertising keywords for selectingadvertisements for participation in the auction.

The concept term scoring system 100 includes a deep network 106 and aclassifier 112. The deep network 106 is a machine learning system thatincludes a set of embedding functions 108 and one or more hidden neuralnetwork layers 110, each having a respective set of parameters. Each ofthe embedding functions 108 receives a respective feature of arespective type and, in accordance with a set of parameters, applies atransformation to the feature that maps the feature into a numericrepresentation. For example, the embedding functions 108 can apply atransformation to the features 120 to map the features into floatingpoint representations 122. Embedding functions will be described in moredetail below with reference to FIG. 2.

An initial layer of the neural network layers 110 receives as an inputthe floating point representations of the input features generated bythe embedding functions and the neural network layers 110 each apply oneor more respective non-linear transformations to the floating pointrepresentations to generate an alternative representation of the input.For example, the neural network layers 110 can generate alternativerepresentation 124 from floating point representations 122 of thefeatures 120 received from the embedding functions 108. Instead of or inaddition to the neural network layers 110, the deep network 106 mayinclude another group of layers that applies successive linear ornon-linear transformations over some or all of the floating pointrepresentations generated by the embedding functions 108.

The classifier 112 receives the alternative representation generated bythe deep network 106 and predicts a value for each field of a conceptscore vector in accordance with values of parameters of the classifier112. Each of the fields in the concept score vector corresponds to arespective concept term in the set of concept terms. For example, theclassifier 112 can generate a concept score vector 126 from thealternative representation 124. The classifier 112 can be any multiclassor multilabel classifier, e.g., a multiclass logistic regressionclassifier, a multiclass support vector machine classifier, a Bayesianclassifier, and so on. In some implementations, instead of theclassifier 112, the concept term scoring system 100 can include aranking function that orders the concept terms based on the alternativerepresentation 124. The ranking function may be, e.g., a hinge-lossranking function, a pairwise ranking function, and so on.

FIG. 2 is a flow diagram of an example process 200 for scoring conceptterms. For convenience, the process 200 will be described as beingperformed by a system of one or more computers located in one or morelocations. For example, a concept term scoring system, e.g., the conceptterm scoring system 100 of FIG. 1, appropriately programmed, can performthe process 200.

The system obtains features of a resource (step 202). As describedabove, the features are either an ordered or unordered list of tokens orof token-value pairs. Each feature is of a respective feature type,i.e., the list of tokens or token-value pairs that makes up the featureis selected from a vocabulary of possible active feature elements of thefeature type.

The system processes each feature using the embedded function for thefeature type of the feature (step 204) to generate a floating-pointvector representation of the feature. Depending on the feature type andon the implementation, the embedding function for a given feature typecan be any of a variety of embedding functions. The system determinesthe type of the feature by parsing the raw input data received by thesystem for each resource. For example, if a portion of the raw inputdata for a given resource is “URL: www.examplesite.com,” the system canparse the input data to determine that one of the resource features iswww.examplesite.com and that the feature is of a URL feature type.

For example, for a feature type whose features consist of a singletoken, the embedding function may be a simple embedding function. Asimple embedding function maps a single token to a floating pointvector, i.e., a vector of floating point values. For example the simpleembedding function may map the token “cat” to a vector [0.1, 0.5, 0.2]and the token “tablet” to a vector [0.3, 0.9, 0.0], based on currentparameter values of the embedding function, e.g., as stored in a lookuptable.

As another example, for a feature type whose features can potentiallyconsist of a list of two or more tokens, the embedding function may be aparallel embedding function. A parallel embedding function maps eachtoken in a list of tokens to a respective floating point vector andoutputs a single vector that is a concatenation of the respectivefloating point vectors. For example, for an ordered list of tokens“Atlanta,” “Hotel”}, the parallel embedding function may map “Atlanta”to a vector [0.1, 0.2, 0.3] and “Hotel” to [0.4, 0.5, 0.6], and thenoutput [0.1, 0.2, 0.3, 0.4, 0.5, 0.6]. In order to obtain the respectivefloating point vectors, the parallel embedding function may use a singlelookup table or multiple different lookup tables.

As another example, for a feature type whose features can potentiallyconsist of a list of two or more tokens, the embedding function may be acombining embedding function. A combining embedding function maps eachtoken in the list to a respective floating point vector and then mergesthe respective floating point vectors into a single merged vector. Thecombining embedding function can merge the respective floating pointvector using a linear function, e.g., a sum, average, or weighted linearcombination of the respective floating point vectors, or using anonlinear function, e.g., a component-wise maximum or a norm-constrainedlinear combination, for example. In order to identify the respectivefloating point vectors, the parallel embedding function may use a singlelookup table or multiple different lookup tables. For example, for theordered list {“Atlanta”, “Hotel”}, the parallel embedding function maymap “Atlanta” to a vector [0.1, 0.2, 0.3] and “Hotel” to [0.4, 0.5,0.6], and then output the sum of the two vectors, i.e., [0.5, 0.7, 0.9].

As another example, for a feature type whose features can potentiallyconsist of a list of two or more tokens, the embedding function may be amixed embedding function. A mixed embedding function maps each token ina list of tokens to a respective floating point vector and generates aninitial vector that is the concatenation of the respective floatingpoint vectors. The mixed embedding function then merges the respectivefloating point vectors into a merged vector and concatenates the mergedvector with the initial vector. For example, for the ordered list{“Atlanta”, “Hotel”}, the mixed embedding function may output aconcatenation of the vectors output by the parallel embedding functionand the combining embedded function, i.e., [0.1, 0.2, 0.3, 0.4, 0.5,0.6, 0.5, 0.7, 0.9].

Depending on the implementation, the system may utilize two differentkinds of embedding functions for two different feature types, and thetwo embedding functions may or may not share parameters. For example,the system may utilize a combining embedding function for a firstfeature type and a mixed embedding function for a second feature type.

If one or more of the features of the resource are not discrete, priorto processing the feature using an embedding function, the system uses ahashing function to hash each non-discrete feature. The system can thenpartition each hashed feature into one of a pre-determined set ofpartitions, and process a value corresponding to the partition using theembedding function for the feature. Additionally, if a particularfeature cannot be obtained for a given resource, that system can mapthat feature to a pre-determined value.

In some implementations, instead of floating point values, a givenembedding function may generate a different kind of numeric values. Forexample, the embedding function may generate quantized integer valueswhose encoding represents floating point values.

The system processes the floating-point vector representations using oneor more neural network layers (step 206). The one or more neural networklayers include one or more layers of non-linear transformations, witheach transformation being defined based on values of a respective set ofparameters. In general, the one or more neural network layers generatean alternative representation of the input based on the floating-pointvector representations of the features of the input. Optionally, thesystem can then process the alternative representation using a sparsebinary output layer, e.g., a layer that outputs a vector that is 0 or 1at every position. An example technique for processing thefloating-point representations using neural network layers is describedin Ruslan Salakhutdinov & Geoffrey Hinton, Semantic hashing,International Journal of Approximate Reasoning, 50 (2009) 969-978.However, many different techniques and mechanisms for processing therepresentations using neural network layers can be used.

The system processes the alternative representation of the input using aclassifier (step 208) to predict an output for each of a set of conceptterms. The classifier predicts the output based on values of a set ofparameters and the alternative representation. The output for a givenconcept term is a prediction of the value of a variable that correspondsto the concept term, e.g., a score for the concept term that representsthe predicted relevance of the concept described by the term to theresource. In some implementations, the system can process thealternative representation of the input using a ranking function insteadof a classifier to predict a ranking of the concept terms according totheir predicted relevance to the concept.

Once the scores for the concept terms are generated, the system canstore the scores in a data store or use the scores for another immediatepurpose. In some implementations, i.e., in the online advertisingcontext, the system can select a specified number of one or morehighest-scoring concept terms or each concept term having a score thatsatisfies a threshold value as advertising keywords to be used inselecting candidate advertisements for participation in an onlineadvertising auction. In some implementations, the selected keywords areused in combination with keywords produced using other techniques toselect the candidate advertisements.

Optionally, prior to making use of the selected concept terms, thesystem can filter out any concept terms that fail to meet one or moreselection criteria. For example, the system may filter out concept termsthat are in a language that does not match the language of the resource,e.g., by comparing data that identifies the language of the resource todata identifying the language of the concept term and filtering out theconcept term when the data does not indicate a match. As anotherexample, the system may filter out concept terms that have a TermFrequency Inverse Document Frequency (TF-IDF) score that exceeds athreshold value. That is, the system may filter out concept terms thathave a high likelihood of being selected because they are popular termsrather than because they are particularly relevant to the resource.

The process 200 can be performed to predict scores for concept terms foran input for which the desired scores are not known.

The process 200 can also be performed on inputs in a set of trainingdata, i.e., a set of inputs for which the output that should bepredicted by the system is known, in order to train the system, i.e., todetermine optimal values for the parameters of the classifier and thedeep network. For example, the process 200 can be performed repeatedlyon inputs selected from a set of training data as part of abackpropagation training technique that determines optimal values foreach of the parameters. Training a concept term scoring system will bedescribed in more detail below with reference to FIG. 3.

FIG. 3 is a flow diagram of an example process 300 for training aconcept term scoring system. For convenience, the process 300 will bedescribed as being performed by a system of one or more computerslocated in one or more locations. For example, a concept term scoringsystem, e.g., the concept term scoring system 100 of FIG. 1,appropriately programmed, can perform the process 300.

The system obtains data identifying training resources and associatedconcept terms for each of the training resources (step 302). Forexample, a concept term may be associated with a resource based on datathat identifies advertisements that received a user selection within apre-determined time window of viewing the resource. For each identifiedadvertisement, the advertising keyword used to place the advertisementin the auction that resulted in the advertisement being presented to theuser can be associated with the resource as a concept term.

The system specifies criteria for the predicted output for each of thetraining resources based on parameters (step 304). That is, for eachresource, the system specifies criteria for the concept term scoresgenerated by the system based on the parameters. For example, theparameters may specify that, for any training resource, the scores forthe concept terms associated with the resource should be higher than anyscore for any other concept term in the set of concept terms or arandomly selected sample of the other concept terms in the set ofconcept terms. Optionally, the parameters may require that the scoresfor the concept terms associated with the resource exceed the otherscores by a threshold value. As another example, the parameters mayspecify that, for any training resource, the scores for the conceptterms associated with the resource should each be higher than aspecified threshold value. As another example, the parameters mayspecify that the concept terms associated with the resource should allbe in a specified number of highest-scoring concept terms. Theparameters used to generate the criteria can be provided to the system,e.g., by a system administrator, and may be static, i.e., predeterminedat the beginning of the training, or dynamic, i.e., can be automaticallyadjusted throughout the training of the system. For example, theparameters may be relaxed during training until the performance of thesystem degrades, and then made more stringent.

The system performs a training process to train the classifier (step306) using the specified criteria and features of the training resourcesfor the parameters and a set of training data. Additionally, thetraining process uses the method of backpropagation to adjust theparameters of all the components of a deep network, e.g., the deepnetwork 106 of FIG. 1.

As part of the training process, if the label predicted by theclassifier for a particular training resource is different from theknown desired label for that particular training resource, i.e., theconcept scores generated by the classifier do not satisfy the criteriafor the training resource, the classifier will adjust its parameters soas to reduce the expected error on that particular input usingconventional gradient based methods. Furthermore, as part of thebackpropagation method, the classifier sends an error signal to the deepnetwork, which allows the deep network to adjust the parameters of itsinternal components and of the set of embedding functions thoughsuccessive stages of backpropagation.

In some circumstances, e.g., for large sets of training data, thetraining process can be parallelized in any of a variety of ways. Forexample, the training process can be parallelized using one or more ofthe techniques for parallelizing the training of a machine learningmodel described in “Large Scale Distributed Deep Networks,” JeffreyDean, et al., Neural Information Processing Systems Conference, 2012.

Embodiments of the subject matter and the functional operationsdescribed in this specification can be implemented in digital electroniccircuitry, in tangibly-embodied computer software or firmware, incomputer hardware, including the structures disclosed in thisspecification and their structural equivalents, or in combinations ofone or more of them. Embodiments of the subject matter described in thisspecification can be implemented as one or more computer programs, i.e.,one or more modules of computer program instructions encoded on atangible non transitory program carrier for execution by, or to controlthe operation of, data processing apparatus. Alternatively or inaddition, the program instructions can be encoded on an artificiallygenerated propagated signal, e.g., a machine-generated electrical,optical, or electromagnetic signal, that is generated to encodeinformation for transmission to suitable receiver apparatus forexecution by a data processing apparatus. The computer storage mediumcan be a machine-readable storage device, a machine-readable storagesubstrate, a random or serial access memory device, or a combination ofone or more of them.

The term “data processing apparatus” encompasses all kinds of apparatus,devices, and machines for processing data, including by way of example aprogrammable processor, a computer, or multiple processors or computers.The apparatus can include special purpose logic circuitry, e.g., an FPGA(field programmable gate array) or an ASIC (application specificintegrated circuit). The apparatus can also include, in addition tohardware, code that creates an execution environment for the computerprogram in question, e.g., code that constitutes processor firmware, aprotocol stack, a database management system, an operating system, or acombination of one or more of them.

A computer program (which may also be referred to or described as aprogram, software, a software application, a module, a software module,a script, or code) can be written in any form of programming language,including compiled or interpreted languages, or declarative orprocedural languages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment. A computer program may, butneed not, correspond to a file in a file system. A program can be storedin a portion of a file that holds other programs or data, e.g., one ormore scripts stored in a markup language document, in a single filededicated to the program in question, or in multiple coordinated files,e.g., files that store one or more modules, sub programs, or portions ofcode. A computer program can be deployed to be executed on one computeror on multiple computers that are located at one site or distributedacross multiple sites and interconnected by a communication network.

The processes and logic flows described in this specification can beperformed by one or more programmable computers executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Computers suitable for the execution of a computer program include, byway of example, can be based on general or special purposemicroprocessors or both, or any other kind of central processing unit.Generally, a central processing unit will receive instructions and datafrom a read only memory or a random access memory or both. The essentialelements of a computer are a central processing unit for performing orexecuting instructions and one or more memory devices for storinginstructions and data. Generally, a computer will also include, or beoperatively coupled to receive data from or transfer data to, or both,one or more mass storage devices for storing data, e.g., magnetic,magneto optical disks, or optical disks. However, a computer need nothave such devices. Moreover, a computer can be embedded in anotherdevice, e.g., a mobile telephone, a personal digital assistant (PDA), amobile audio or video player, a game console, a Global PositioningSystem (GPS) receiver, or a portable storage device, e.g., a universalserial bus (USB) flash drive, to name just a few.

Computer readable media suitable for storing computer programinstructions and data include all forms of non-volatile memory, mediaand memory devices, including by way of example semiconductor memorydevices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks,e.g., internal hard disks or removable disks; magneto optical disks; andCD ROM and DVD-ROM disks. The processor and the memory can besupplemented by, or incorporated in, special purpose logic circuitry.

To provide for interaction with a user, embodiments of the subjectmatter described in this specification can be implemented on a computerhaving a display device, e.g., a CRT (cathode ray tube) or LCD (liquidcrystal display) monitor, for displaying information to the user and akeyboard and a pointing device, e.g., a mouse or a trackball, by whichthe user can provide input to the computer. Other kinds of devices canbe used to provide for interaction with a user as well; for example,feedback provided to the user can be any form of sensory feedback, e.g.,visual feedback, auditory feedback, or tactile feedback; and input fromthe user can be received in any form, including acoustic, speech, ortactile input. In addition, a computer can interact with a user bysending documents to and receiving documents from a device that is usedby the user; for example, by sending web pages to a web browser on auser's client device in response to requests received from the webbrowser.

Embodiments of the subject matter described in this specification can beimplemented in a computing system that includes a back end component,e.g., as a data server, or that includes a middleware component, e.g.,an application server, or that includes a front end component, e.g., aclient computer having a graphical user interface or a Web browserthrough which a user can interact with an implementation of the subjectmatter described in this specification, or any combination of one ormore such back end, middleware, or front end components. The componentsof the system can be interconnected by any form or medium of digitaldata communication, e.g., a communication network. Examples ofcommunication networks include a local area network (“LAN”) and a widearea network (“WAN”), e.g., the Internet.

The computing system can include clients and servers. A client andserver are generally remote from each other and typically interactthrough a communication network. The relationship of client and serverarises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of anyinvention or of what may be claimed, but rather as descriptions offeatures that may be specific to particular embodiments of particularinventions. Certain features that are described in this specification inthe context of separate embodiments can also be implemented incombination in a single embodiment. Conversely, various features thatare described in the context of a single embodiment can also beimplemented in multiple embodiments separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various system modulesand components in the embodiments described above should not beunderstood as requiring such separation in all embodiments, and itshould be understood that the described program components and systemscan generally be integrated together in a single software product orpackaged into multiple software products.

Particular embodiments of the subject matter have been described. Otherembodiments are within the scope of the following claims. For example,the actions recited in the claims can be performed in a different orderand still achieve desirable results. As one example, the processesdepicted in the accompanying figures do not necessarily require theparticular order shown, or sequential order, to achieve desirableresults. In certain implementations, multitasking and parallelprocessing may be advantageous.

What is claimed is:
 1. A method performed by one or more computers, themethod comprising: receiving an input comprising a plurality of featuresof a resource, wherein each of the features is of a different featuretype; generating an alternative representation of the features of theresource, comprising: generating a respective numeric representation ofeach the features by processing each of the features using a respectiveembedding function, wherein each of the embedding functions is specificto features of a respective feature type, and processing the respectivenumeric representations through one or more neural network layers togenerate the alternative representation; and providing the alternativerepresentation of the features of the resource as input to a neuralnetwork classifier for classification of a relevance of a plurality ofconcept terms to the resource.
 2. The method of claim 1, wherein theneural network classifier is configured to: process the alternativerepresentation of the features of the resource to generate a respectiverelevance score for each of the plurality of concept terms, wherein eachof the respective relevance scores measures a predicted relevance of thecorresponding concept term to the resource.
 3. The method of claim 1,wherein the numeric representations are vectors of floating pointvalues.
 4. The method of claim 1, wherein the numeric representationsare vectors of quantized integer values, and wherein an encoding of thequantized integer values represents floating point values.
 5. The methodof claim 1, further comprising: obtaining the plurality of features ofthe resource in response to receiving an indication that an onlineadvertisement auction is to be conducted to select one or moreadvertisements for inclusion in a particular presentation of theresource.
 6. The method of claim 5, further comprising: selecting one ormore of the concept terms as advertising keywords to be used inselecting candidate advertisements for participation in the onlineadvertisement auction based on the classification of the relevance ofthe concept terms to the resource.
 7. The method of claim 1, wherein aparticular feature of the plurality of features is not discrete, andwherein the method further comprises: hashing the particular feature togenerate a hashed feature; partitioning the hashed feature into aparticular partition of a predetermined set of partitions; andprocessing a value corresponding to the particular partition using theembedding function for the feature.
 8. A system comprising one or morecomputers and one or more storage devices storing instructions that whenexecuted by the one or more computers cause the one or more computers toperform operations comprising: receiving an input comprising a pluralityof features of a resource, wherein each of the features is of adifferent feature type; generating an alternative representation of thefeatures of the resource, comprising: generating a respective numericrepresentation of each the features by processing each of the featuresusing a respective embedding function, wherein each of the embeddingfunctions is specific to features of a respective feature type, andprocessing the respective numeric representations through one or moreneural network layers to generate the alternative representation; andproviding the alternative representation of the features of the resourceas input to a neural network classifier for classification of arelevance of a plurality of concept terms to the resource.
 9. The systemof claim 8, wherein the neural network classifier is configured to:process the alternative representation of the features of the resourceto generate a respective relevance score for each of the plurality ofconcept terms, wherein each of the respective relevance scores measuresa predicted relevance of the corresponding concept term to the resource.10. The system of claim 8, wherein the numeric representations arevectors of floating point values.
 11. The system of claim 8, wherein thenumeric representations are vectors of quantized integer values, andwherein an encoding of the quantized integer values represents floatingpoint values.
 12. The system of claim 8, the operations furthercomprising: obtaining the plurality of features of the resource inresponse to receiving an indication that an online advertisement auctionis to be conducted to select one or more advertisements for inclusion ina particular presentation of the resource.
 13. The system of claim 12,the operations further comprising: selecting one or more of the conceptterms as advertising keywords to be used in selecting candidateadvertisements for participation in the online advertisement auctionbased on the classification of the relevance of the concept terms to theresource.
 14. The system of claim 8, wherein a particular feature of theplurality of features is not discrete, and wherein the method furthercomprises: hashing the particular feature to generate a hashed feature;partitioning the hashed feature into a particular partition of apredetermined set of partitions; and processing a value corresponding tothe particular partition using the embedding function for the feature.15. One or more non-transitory computer storage media storinginstructions that when executed by one or more computers cause the oneor more computers to perform operations comprising: receiving an inputcomprising a plurality of features of a resource, wherein each of thefeatures is of a different feature type; generating an alternativerepresentation of the features of the resource, comprising: generating arespective numeric representation of each the features by processingeach of the features using a respective embedding function, wherein eachof the embedding functions is specific to features of a respectivefeature type, and processing the respective numeric representationsthrough one or more neural network layers to generate the alternativerepresentation; and providing the alternative representation of thefeatures of the resource as input to a neural network classifier forclassification of a relevance of a plurality of concept terms to theresource.
 16. The computer storage media of claim 15, wherein the neuralnetwork classifier is configured to: process the alternativerepresentation of the features of the resource to generate a respectiverelevance score for each of the plurality of concept terms, wherein eachof the respective relevance scores measures a predicted relevance of thecorresponding concept term to the resource.
 17. The computer storagemedia of claim 15, wherein the numeric representations are vectors offloating point values.
 18. The computer storage media of claim 15,wherein the numeric representations are vectors of quantized integervalues, and wherein an encoding of the quantized integer valuesrepresents floating point values.
 19. The computer storage media ofclaim 15, the operations further comprising: obtaining the plurality offeatures of the resource in response to receiving an indication that anonline advertisement auction is to be conducted to select one or moreadvertisements for inclusion in a particular presentation of theresource.
 20. The computer storage media of claim 19, the operationsfurther comprising: selecting one or more of the concept terms asadvertising keywords to be used in selecting candidate advertisementsfor participation in the online advertisement auction based on theclassification of the relevance of the concept terms to the resource.